1. Field of the Invention
This present invention relates generally to the field of integrated circuit manufacturing and, more specifically, to the monitoring of plasma used in the manufacture of integrated circuits.
2. Description of the Related Art
This section is intended to introduce the reader to aspects of the art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In the manufacturing of integrated circuits, numerous microelectronic circuits may be simultaneously manufactured on a semiconductor substrate. These substrates are usually referred to as wafers. A typical wafer is comprised of a number of different regions, known as die regions. When fabrication is complete, the wafer is cut along these die regions to form individual die. Each die contains at least one microelectronic circuit, which is typically replicated on each die. One example of a microelectronic circuit which can be fabricated in this way is a dynamic random access memory.
Although referred to as semiconductor devices, integrated circuits are in fact fabricated from numerous materials of varying electrical properties. These materials include insulators or dielectrics, such as silicon dioxide, and conductors, such as aluminum, tungsten, copper, and titanium in addition to semiconductors, such as silicon and germanium arsenide. By utilizing these various materials, the various transistors, gates, diodes, vias, resistors, and connective paths comprising the integrated circuit may be formed. Because of the complexity, both in materials and in design, incorporated into integrated circuits, the integrated circuit can be designed to perform a variety of functions within a limited space.
In manufacturing these complex integrated circuits, plasmas may be generated and used to facilitate different aspects of the process. For example, plasmas may be used to facilitate the deposition of one or more of the layers comprising the integrated circuit. In particular, plasma enhanced chemical vapor deposition (PECVD) may be used to deposit layers or films of silicon nitride (SixNy), silicon oxide (SixOy), silicon oxide nitride (SixOyNz), as well as metals, such as titanium, and metal-containing films, such as titanium nitride (TiN). In addition, plasmas may be used to facilitate the etching of fine structures in a layer of material on a substrate.
In addition to depositing the desired materials as layers on the substrate, the deposition process may result in layers of material being deposited on the exposed surfaces of the deposition chamber. If left to accumulate, the materials deposited on the surfaces of the chamber may eventually chip or “spall” off as particles or flakes which can contaminate future deposition processes. Therefore, a plasma may also be used to clean or etch the chamber surfaces periodically to prevent accumulations of the deposited materials on the chamber surfaces.
The plasma itself is a partially ionized gas comprising highly reactive radicals and ions. The highly reactive radicals and ions comprise the reactive species needed to perform the desired deposition, etching, or cleaning processes and are typically generated from the disassociation of precursor molecules. Examples of precursor molecules include, but are not limited to, silane (SiH4), germane (GeH4), ammonia (NH3), phosphine (PH3), nitrogen trifluoride (NF3), titanium chloride (TiCl4), tantalum chloride (TaCl5), molybdenum hexafluoride (MoF6), tetraethyl orthosilicate (TEOS) (Si(OC2H5)4) and tungsten fluoride (WF6).
In a deposition context, the reactive radicals and/or ions generated from the disassociation of the precursor may interact with a substrate surface, such as a wafer, to form a layer of solid material on the surface. For example, silane or tetraethyl orthosilicate are precursors which, in conjunction with oxygen, may be used to deposit silicon dioxide on a substrate. By contrast, in an etching or cleaning context, the reactive radicals and/or ions generated from the disassociation of the precursor may interact with deposited material to break down the deposited material into various gaseous byproducts which may then be flushed from the reactor. For example, nitrogen trifluoride is a precursor which, upon disassociation, is effective at etching or removing silicon dioxide.
The plasma to be used in these processes may be generated by various means. For example, a plasma may be generated by applying sufficient voltage, typically an AC or RF voltage, between two electrodes. Alternately, microwaves may be used to generate the plasma by heating the electrons of the precursor, thereby inducing atomic collisions which lead to precursor disassociation and plasma formation. A magnetron may be used to generate the microwave energy used to produce the plasma.
The successful generation of the plasma during the processes discussed above may be determined by an optical detector positioned in a viewport or window of the applicator. In particular, the optical detector may measure light emission within the reactor and, based on some threshold, may thereby determine if a plasma has been formed. However, in some instances, it has been found that the detector threshold may be exceeded, thereby indicating the presence of a plasma, when the plasma is insufficient or inadequate for the desired task. For example, a precursor may be sufficiently disassociated to register as a plasma, but insufficiently disassociated to actually perform the desired function, such as deposition, etching, or cleaning. Such an unsuitable plasma may arise due to magnetron tube age, deterioration in a microwave-based system, or electrode fouling in a RF or voltage system.
Regardless of the cause of the plasma deficiency, however, the failure of the optical detector to warn of an unsuitable plasma may lead to wasted time and/or resources if the failure of the plasma facilitated processes is not otherwise recognized. In particular, the optical detector may fail to detect the unsuitability of the plasma for an indefinite period before the plasma quantity or quality deteriorates below the configured threshold to generate an error or warning message. It is therefore desirable to determine more accurately when a plasma is unsuitable to facilitate a desired process, such as a deposition, etching, or cleaning process, and thereby to minimize the problems arising due to the plasma deficiency.